A restoration of hopelessly mired Kaatedocus in what is now Wyoming's Jurassic Howe Quarry. Art courtesy Sauriermuseum Aathal.

The Late Jurassic was the heyday of dinosaur giants. Apatosaurus, Barosaurus, Brachiosaurus, and Diplodocus were gargantuan, long-necked sauropods that reached lengths in excess of 70 feet, and some, such as Supersaurus and the diplodocid formerly known as “Seismosaurus”, stretched even longer. But what’s even more startling is that many of these massive dinosaurs were neighbors who trod among fern-covered floodplains dotted by swaths of conifer forest. These habitats, preserved in the American west’s Morrison Formation, must have been some of the most productive ecosystems of all time.

But the enormous sauropods didn’t enjoy an edenic existence. Part of the reason we know so much about them is because of vast graveyards strewn with the jumbled, disarticulated remains of Late Jurassic dinosaurs. Scattered from eastern Utah to southern Montana, these mass death assemblages reflect a harshly seasonal Jurassic climate. Thirsty dinosaurs died in droughts, only to have their dessicated bodies preserved by floodwater-carried sediment when the rains returned.

Dinosaur National Monument, straddling the Utah-Colorado border, is the most famous Jurassic graveyard. But other bonebeds preserve different assemblages of dinosaurs. Wyoming’s Howe Quarry, for one, has traditionally thought to be the resting place of multiple Barosaurus.Well-preserved, articulated sauropod hands and feet hint that the parched herbivores came to this place looking for water, but ended up stuck in the muck. As testified by shed teeth, Allosaurus and other scavengers tore the sauropods apart, and what remained of the unfortunate dinosaurs was quickly buried soon thereafter.

Despite being painstakingly excavated by the famous paleontologists Barnum Brown, Roland T. Bird, and their American Museum of Natural History crews during the 1930s, the Howe Quarry dinosaurs received little attention from succeeding generations of paleontologists. The site seemed to be yet another slurry of sauropod bones from already-known dinosaurs. Yet, in a Journal of Systematic Palaeontology paper, Emanuel Tschopp and Octávio Mateus propose that they have found a previously-unknown dinosaur hiding within the chaotic mix of sauropod bones.

Barnum Brown’s crew was the first to systematically work the Jurassic rock around Shell, Wyoming for dinosaur bones, but they were not the last to do so. “Big Al”, a young Allosaurus that belongs to an as-yet-undescribed species, was found in close proximity to the Howe Quarry, and excavations by Switzerland’s Sauriermuseum Aathal turned up additional parts of the original site. Among the bones recovered by the Swiss team were a series of neck vertebrae associated with a partial, disarticulated skull. These were previously considered to be from a juvenile Diplodocus or Barosaurus, but Tschopp and Mateus argue that the bones represent a new diplodocid dinosaur they have named Kaatedocus siberi.

The reconstructed head and upper neck of Kaatedocus. Photo courtesy Sauriermuseum Aathal.

In general appearance, Kaatedocus wasn’t much different from Diplodocus and Barosaurus. All of these dinosaurs were long-tailed sauropods with long, low skulls with muzzles tipped with peg teeth. The features that make Kaatedocus distinct, Tschopp and Mateus suggest, are subtle characteristics in the skull and vertebrae, such as a U-shaped notch between the frontal bones and the minor degree of separation between the neural spines along some neck vertebrae, among other details. Based on the suite of apparently unique characteristics, the researchers suggest that their Kaatedocus specimen was a relatively small, subadult animal that was about 46 feet long when it perished.

Yet Tschopp and Mateus also point out that the skull of Kaatedocus resembles that of a juvenile diplodocid sauropod. The orbit, or eye opening, is large, and the dinosaur had a rounded muzzle with an expanded tooth row also seen in the skull of a juvenile Diplodocus described by John Whitlock and coauthors in 2010. The skull of Kaatedocus is shallower and more slender than the juvenile Diplodocus skull, but, given the size of the animal and the juvenile characteristics, I have to wonder if Kaatedocus is really a relatively young individual of Barosaurus or another previously-named sauropod. What might seem to be a distinctive combination of characteristics could be a sign that the dinosaur was still changing as it approached maturity.

Kaatedocus could be a distinct form of sauropod that inhabited Jurassic environments in the little-known northern part of what is now preserved in the Morrison Formation. Or maybe it’s an immature Barosaurus or Diplodocus. Context will be essential to testing these ideas.

The authors of the new study argue that Kaatedocus was found relatively low in the Morrison Formation, earlier than 147 million years ago. If this is accurate, perhaps Kaatedocus seems archaic because it actually lived before derived sauropods like Barosaurus and Diplodocus in a swath of northern ecosystems that evolved as the ancient Sundance Sea drained off the continent. When paleontologists Jerry Harris and Peter Dodson described Suuwassea emilieae – a cousin of Diplodocus and possibly a contemporary – from bones found in Montana, they proposed that the “northern end of the Morrison Formation depositional basin may contain a unique fauna from a heretofore unrecognized paleoecosystem that contrasts with the general portrait of the formation’s fauna based on material from outcrops south of the Bighorn Basin.” Then again, geologic studies have yet to fully resolve the ages and relationships of the various Howe Quarry excavations, and the rarity of definite Barosaurus material hampers attempts to compare Kaatedocus with the previously-discovered species.

The perplexing nature of Kaatedocus underscores the fact that, despite their familiarity, there’s much we still don’t know about Morrison Formation dinosaurs and their relationships. In fact, how these Jurassic environments could have supported such startling arrays of dinosaurs is one of the biggest mysteries of all. Bonebeds concentrate clues that may help us understand this ecological enigma, and better understand a time when titans roamed the earth.

Wilborn, B. 2001. Two new dinosaur bonebeds from the Late Jurassic Morrison Formation, Bighorn Basin, WY: An analysis of the paleontology and stratigraphy. Unpublised master’s thesis, Virginia Polytechnic Institute and State University. i-44.

There are 17 Comments. Add Yours.

Thomas Holtz
December 18, 2012

Firstly, congrats on the new home for Laelaps! Secondly, I agree that this new specimen is quite likely a juvenile Barosaurus. We’ve seen so often in recent years the degree of change possible in the ontogeny of dinosaurs, and I think this may yet be another example. The AMNH has juvenile Barosaurus material, which definitely deserve a comparative study with the Kaatedocus specimen.

Hikaru Amano
December 18, 2012

I fully agree with Dr. Holtz here…the specimens being in subadult phase makes the case that Kaatedocus is the subadult phase of Barosaurus. It’s awfully similar in morhology to subadult Diplodocus skull….

Jim Kirkland
December 18, 2012

Congratulations Brian. I’ll be following you and Carl for sure.
I got the paper yesterday (always a day late and a dollar short at the survey) and noted that they mentioned that the Howe Quarry material that Brown excavated was never described and much of it was destroyed. Because of this they briefly speculate that all the “Diplodocus and Barasaurus” material from this quarry may be Kaatedocus. Reexamining what is left at the AMNH is clearly warranted. Also the age of the Howe Quarry is a item of concern. They report it as below the “clay-change” (which I have noted is probably an unconformity), but it is reported that clay change is lost going north in Wyoming, although there was a dinosaur species typically found below the clay-xchange was found near Howe Quarry; I would say determining the age of the Howe Quarry is critical in all of this.
Once again, an interesting paper raises more questions.

Brian Switek
December 18, 2012

Thanks for the comments, everyone. I’m glad to hit the ground running with a contentious sauropod, hah.

I’m inclined to agree that “Kaatedocus” is indeed a young Barosaurus, although I wanted to be fair in presenting the case in the new paper. Clearly, as Jim points out, there’s a lot of work to be done here – we need a better understanding of northern Morrison Formation stratigraphy, as well as comparison and additional study of the Howe Quarry material. Hopefully the description of this young sauropod will inspire some additional research into this highly-productive bonebed.

All that aside, though, it’s amazing that there are so many Morrison Fm. bonebeds to study. Late Jurassic dinosaurs lived large, but definitely didn’t have it easy.

Kyle
December 18, 2012

If Thomas Holtz says it’s a juvenile Barosaurus, it’s a juvenile Barosaurus. Guess we won’t be seeing Kaatedocus in his book

Don Pfister
December 18, 2012

I am curious to know if the teeth of Kaatedocus were simply pencil-like, or did they have grooves along the edges? Also, do all the diplodocids have the same number of teeth in the skull parts?

emanuel tschopp
December 19, 2012

First of all, what an honour to be subject of the first blog post of the returned Laelaps! Thanks, Brian!
Concerning the juvenile Barosaurus, there are a few things to say.
First of all, nobody knows really if Barosaurus is common at the Howe Quarry. None of the specimens found there has yet been really identified scientifically. It
was Barnum Brown, who shortly noted that most of the skeletons at Howe Quarry
probably were Barosaurus, but without justifying the statement. Based on this, the AMNH catalogued the neck and partial skull they have on display as Barosaurus, but nobody has ever looked at this in detail. Given that the northern exposures of the Morrison Formation are understudied compared to the South, and given that they also yielded Suuwassea recently, it should not be excluded a priori that there might be more new species coming from the North. The differences between the ‘valid’ species of diplodocines are extremely subtle, in the tail vertebrae it is even difficult to distinguish between Barosaurus and Diplodocus, especially if you look t the holotypes of Diplodocus longus and Barosaurus lentus.
Juvenile – no. Even though the skull has a lot of juvenile features, this is the same for Tornieria, and many of them are shared with Dicraeosauridae, so the question remains if they are plesiomorphies or early ontogeny. The latter, however can be excluded by the complete fusion of cervical centra, neural arches and cervical ribs, which clearly points to an adult individual, otherwise you should be able to see at least the suture lines, which is not the case in the holotype. So, subadult is probably a more accurate description of the ontogenetic age. And between subadults and adults, morphological changes should be minor. One of these proposed morphological changes concern the elongation of the neck vertebrae, which are supposed to get longer during ontogeny. However, especially ‘juvenile’ Barosaurus with its extremely elongated centra (EI > 5, usually) is a highly improbable identification for a specimen that has ratios approaching the (short) ones of Apatosaurus. If you have a look at the paper, you’ll see that there are several more differences between Kaatedocus and both the holotype of Barosaurus lentus, as well as the best-preserved specimen, which is on display at the American Museum.
Concerning the Howe Quarry, there are other, similarly sized specimens (like SMA 0004) in the Howe Quarry with more elongate neck verts, so maybe those will prove to be more closely related to (or juvenile) Barosaurus, but this will be part of my PhD thesis, so I can’t tell you much more now.
So, stay tuned, and thanks again for covering our paper!

emanuel tschopp
December 19, 2012

and, by the way, the reconstruction of made by Davide Bonadonna

Mike Taylor
December 19, 2012

Woah, everyone!

Tom said;

“Secondly, I agree that this new specimen is quite likely a juvenile Barosaurus.”

At this point, I don’t agree, and I can tell you that Matt Wedel doesn’t either. I don’t want to say too much here, both because we’ll be SV-POW!ing this paper and because I don’t want to tread on Matt’s toes.

But let’s not all be so hasty with the ontogenetic synonymising.

kylee
December 19, 2012

This is an incredible find and story.Do you think there is a possibility that the creature might be the first relative to the evolution of sauropods or maybe a hybrid species? I hope you find more evidence to clear up the conclusion.

Thomas R. Holtz, Jr.
December 21, 2012

Don’t be too hasty in assuming it won’t be in the updated appendix to the book. In the comments I might say something about possible synonymy, but I’ll still give it its own listing!

The whole issue of species-level diversity in Morrison sauropods needs a good going over. For example, it might be that Kaatedocus turns out to be a valid genus, but winds up being synonymous with a diplodocid species currently listed in one of the other species.

Dear Brian,
Often, when reading articles such as this, it is related that the herd wandered in to a swamp, got trapped and died. This would seem to be common explanation. It occurs to me, however, that there may an alternative to the ‘swamp’ detail; Is it a possibility that there was, in some cases, an earthquake that caused severe liquifaction, thereby engulfing these unfortunate creatures? After all, when was the last time we learned of a herd of large quadrupeds, gnu, buffalo, etc., all wandering (or even chased!) in to a swamp and drowning in modern times? Surely seismic liquifaction, in low-lying areas, must have claimed many creatures over the eons. Has this ever been considered?
Just a thought.
Philip.

Andy Hall
January 14, 2013

The skull and neck of a new flagellicaudatan sauropod from the Morrison Formation and its implication for the evolution and ontogeny of diplodocid dinosaurs by E. Tschopp and O. Mateus is now free to read at http://ow.ly/gMzti

[…] dinosaur’s flanks and back some imposing decoration. And “Somehow all those sympatric Morrison [Formation] sauropods species were able to sort out whom to mate with,” Witmer says. Just because sauropods were probably […]

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